Tape laminates for diaper closure

ABSTRACT

A composite pre-laminated tape is provided having at least one tape backing (13) of a porous paper coated on one face with a release coating (15) of a solventless, radiation-cured silicone applied directly to the paper.

TECHNICAL FIELD

This invention relates to tape laminates and in particular to compositepre-laminated tapes for forming closures, e.g., for disposable diapers.

BACKGROUND AND FIELD OF THE INVENTION

At least as early as 1955, it had been suggested to use trips ofnormally tacky and pressure-sensitive adhesive tape to secureconventional cloth diapers on an infant, see for example U.S. Pat. Nos.2,714,889 and 3,221,738. A few years later, when disposable diapersbecame extremely popular, strips of pressure-sensitive adhesive tapewere again employed as closures, see for example U.S. Pat. No.3,620,217.

A disposable diaper typically has a thin, flexible, low densitypolyethylene film cover, an absorbent filler within the cover, and aporous inner liner overlying the filler. The diaper is positioned at thecrotch of an infant with the two ends of the diaper extending toward thefront and back, respectively. Edges on each side of the diaper are theneither positioned adjacent to each other or overlapped using a strip ofpressure-sensitive adhesive tape being adhered to the cover film atborder regions adjacent each of the two edges to hold the diaper closed.

After a tape closure has been opened, it is frequently discovered thatthe diaper has not been soiled and hence that there is no need toreplace it. If the diaper cover has not been torn, a second strip oftape can sometimes be applied as a replacement closure, but this isoften inconvenient. As a result, considerable work has been undertakento develop a tape diaper closure that is not only capable of bondingfirmly to the diaper cover but is also capable of being opened withoutdestroying the tape diaper closure or the diaper cover and subsequentlyreclosed. Closures of this type have involved a combination of two ormore tapes, one of which remains permanently adhered to one edge of thediaper and the other being removably adhered to the other edge of thediaper. Examples of such products are disclosed in U.S. Pat. Nos.3,951,149, 3,987,793, 3,999,546, 4,020,842, 4,227,530, 4,726,971 and4,801,480, and European Patent No. 0148587A.

Typically, tape closures for diapers are fabricated by positionablymounting a plurality of individual rolls of the appropriate tapes andcombining then in situ to form a composite strip of tape, the width ofwhich is substantially the same as the length of the diaper closure tobe fabricated. The composite roll is then severed at right angles to theedges of the composite strip at intervals corresponding to the width ofthe desired tape closure and adhered at an appropriate location alongthe border adjacent the side edges of the diaper as exemplified in U.S.Pat. Nos. 3,616,114, 4,726,971 and 4,801,480, and European Patent no.0148487A. Although this manufacturing process is effective, relativelysophisticated machinery is necessary to accomplish the superimpositionof several rolls of tape to form a composite strip of tape in situ.Thus, it is desirable to provide diaper manufacturers with a compositepre-laminated tape in a single roll from which tape closures may readilybe prepared.

A common feature of such tape closure systems is that the fastening orclosure tape comprises a backing, such as paper, polymeric film etc.,having an adhesive layer on one side and a coating of a suitable releaseagent on the other side to facilitate unwinding of the composite stripwhen wound upon itself about a core. Generally, the backing comprisespaper which is coated with a barrier layer prior to application of therelease agent in the form of a solution or water-based formulation. Thebarrier layer prevents the formulation of release agent being absorbedby the porous paper prior to drying thereby ensuring the release agentremains at the surface where it is most effective. Suitable materialsfor the barrier layer include polyethylene, typical release agents arebased on silicone chemistry.

Solventless, radiation-curable release coating compositions are knownand are disclosed, for example, in British patent No. 2010698. Thecompositions may be applied and cured on any suitable substrateincluding paper, wood, metals, plastics materials, ceramics, glass,concrete etc. The Examples illustrate the release coating being appliedto 40 pound (18 kg) super-calendared kraft paper.

European Patent Application No. 0315297 discloses that in order toemploy radiation-curable silicone coatings on porous and lightlymoisture-absorbent paper substrates it is necessary to employ a barriercoating or radiation-insensitive hot melt material e.g a wax-likematerial. The use of the hot melt wax-like material allows poor grade,porous papers to be successfully coated with radiation-curable siliconeand pressure-sensitive adhesive tapes may be formed from such releasecoated paper.

It has now been found that pressure-sensitive adhesive tapes suitablefor use in closure systems may comprise a backing of paper coateddirectly with a solventless radiation-cured release coating.

Therefore, according to the present invention, there is provided alaminate tape construction comprising two or more tapes each having alayer of pressure-sensitive adhesive in which at least one of the tapescomprises a paper backing having, on the opposite side to said adhesivelayer, a release coating of a solventless, radiation-cured siliconeapplied directly to the paper.

The laminate tape construction of the invention is suitable for closuresystem, particularly for diapers, with at least the fastening tapehaving the radiation-cured release coating.

The application of the release coating directly to the paper backing hasseveral advantages, including:

1. lower cost backings may be used because of the elimination of onemanufacturing process, film extrusion or lamination of the barrier layerand its associated waste.

2. improved degradability due to the elimination of the barrier layer,such as polyethylene, allowing direct access to the paper fibres throughthe silicone alone.

3. eliminates or reduces need for pretreatment by corona discharge ofthe paper prior to silicone coating.

4. eliminates the risk of product failure by delamination at the paperbarrier layer interface.

The paper backing provides the basic strength of the tape. A clupakpaper provides the combination of strength, extensibility orconformability and reasonable tear resistance to suit the needs of theapplication. The lamination or extrusion of a barrier layer e.g.polyethylene or similar polymer film, to the surface provides solely anon-porous surface for subsequent coatings. It does not materiallyaffect the properties described above.

A suitable paper will typically be bleached for the aestheticrequirements of a hygiene application but an unbleached (brown),semi-bleached (beige or buff) or colored paper would also be functional.

A range of paper basis weight of 50 to 150 g/m² is suitable, typically80 to 110 g/m².

The elimination of the barrier layer on the paper requires that therelease coating laid down must be cured and thus non-migratory in a veryshort time, before any significant penetration into the paper can occur.

In accordance with the invention, the curing of the solventless siliconebegins essentially immediately. If the cure were thermally actuated, aperiod of 5 to 60 seconds could be necessary to achieve fullcross-linking or cure. If, however, the cure is radiation activated,either by electron beam or ultra violet radiation, the curing processwill proceed in a fraction of a second. The advantage of this is thatthe silicone coating will not have a chance to effectively penetrate thepaper before being fixed by the cure mechanism. Higher cure rates permithigher run speeds which in turn means the coated paper is transported tothe cure module faster thus further reducing the opportunity forabsorption. Typical silicone systems are those commercially availablefrom Goldschmidt, Essen of Germany; General Electric of U.S.A; WackerChemie of Germany and Dow Corning of U.S.A.

The coating weight of the silicone fluid should be in the range of 0.4to 2.0 g/m² to provide a continuous coating that satisfactorily permitsthe subsequent unwinding of a roll of tape whose adhesive is directly incontact with the silicone coating on the lap below.

The coating will be such that when one layer of the finished tape issuperimposed upon another, rolled down with a 2 kg or similar weight andthen the upper tape layer is peeled away at 180 degrees, the forcerequired shall be between 0.1 and 3.0 newtons per 25 mm width.

The base paper, as supplied in roll form, may be printed with either afull coating to produce a colored surface or with a definitive legend toidentify it or its use. Appropriate printing methods include flexographyor rotogravure utilizing commercially available water, solvent-based orsolventless inks. Subsequently, the printed or unprinted paper may becorona treated if desired to pretreat the surface to be silicone coated.

The silicone coating may then be applied by commercially availablecoating stations using the principle of multi-roll gravure coating toachieve the low coating weights required. A typical coating stationwould use from 3 to 6 coating rolls.

As close as possible to the last nip (the coating nip) of the siliconecoating station should be the radiation curing station. This stationcomprises a source of radiation, typically either ultraviolet orelectron beam, directed towards the coated web travelling past. In theevent of UV-curing, it may be necessary to also have an inert gasatmosphere above the surface to prevent inhibition of cure byatmospheric oxygen. Typically, this atmosphere is nitrogen.

Subsequently, the siliconized paper may be coated with an adhesive masseither by the application of a hot melt adhesive and subsequent coolingor by the application of a solvent based adhesive of sufficiently highsolids content and viscosity that the adhesive does not penetrate thepaper surface to any significant degree.

This fastening tape produced as above would be slit to the desired sizeand then combined with one or two other tapes, e.g., a release tape anda target tape optionally together with fingerlift(s) and a centre stripeto form the laminate tape construction. A fingerlift facility may alsobe obtained by leaving the edge of paper, e.g., 1 to 6 mm, uncoated withadhesive when the fastening tape is formed.

Examples of laminated tape constructions include:

1. A roll of tape comprising an elongate prelaminated tape compositewound convolutely upon itself about an annular core, especially suitedfor preparing a tape closure for disposable diapers by simply severingsaid elongate prelaminated tape composite parallel to the axis of thecore at intervals corresponding to the predetermined width of saidclosure, the length of each such closure corresponding to the width ofthe roll of tape, said prelaminated tape composite comprising incombination:

a. a fastening tape comprising an elongate strip of sheet backingmaterial, having first and second edges, being substantially as wide assaid tape composite and having a layer of a first normally tacky andpressure-sensitive adhesive coated over substantially one surface ofsaid backing material.

b. optionally, a layer of a second aggressive, normally tacky andpressure-sensitive adhesive coated over approximately one-third of thelayer of said first normally tacky and pressure-sensitive adhesive alongthe first edge thereof.

c. a fingerlift provided on the first pressure-sensitive adhesiveadjacent the second edge thereof.

d. a release tape, having first and second surfaces, the first surfaceadhered to said first pressure-sensitive adhesive layer.

e. a layer of normally tacky and pressure-sensitive adhesive coated overthe second surface of said release tape.

f. a unifying strip centered along the junction of said second adhesivelayer and the adhesive layer on said release tape and adhered to saidadhesive layers, at least one of said tapes comprising a paper backinghaving a release coating of solventless, radiation-cured siliconeapplied directly to the paper. This construction is in accordance withU.S. Pat. No. 4,726,971.

2. A roll of tape comprising an elongated prelaminated tape compositewound convolutely upon itself about an annular core, especially suitedfor preparing a tape closure for disposable diapers by simply severingsaid elongated prelaminated tape composite parallel to the axis of thecore at intervals corresponding to the predetermined width of saidclosure, the length of each such closure corresponding to the width ofthe roll of tape, said prelaminated tape composite comprising incombination:

a. a fastening tape divided into a bonded section and a fasteningsection with the fastening tape comprising an elongated strip of sheetbacking material, having first and second edges, being substantially aswide as said tape composite, and having a first layer of normally tackyand pressure-sensitive adhesive coated over substantially one surface ofsaid backing material.

b. a first fingerlift provided on the first layer of pressure-sensitiveadhesive adjacent the second edge thereof.

c. a target tape, having first and second surfaces, the first surfaceadhered to said first pressure-sensitive adhesive layer.

d. a second layer of normally tacky and pressuresensitive adhesivecoated on the second surface of the target tape.

e. a second fingerlift provided on the second layer of normally tackyand pressure-sensitive adhesive.

f. a release tape having first and second surfaces, the first surfaceadhered to said second pressure-sensitive adhesive layer.

g. a third layer of normally tacky and pressure-sensitive adhesivecoated over the second surface of said release tape.

h. a unifying strip centered over said release tape edge and adhered tothe third adhesive layer and to the first adhesive layer on thefastening tape by folding under the target tape, at least one of saidtapes comprising a paper backing having a release coating ofsolventless, radiation-cured silicone applied directly to the paper.This construction is in accordance with U.S. Pat. No. 4,801,480.

3. A roll of tape as described in (2) with the exception that theunifying strip is not folded under the target tape.

4. A roll of tape comprising a composite elongate strip ofpressure-sensitive adhesive sheet material wound convolutely upon itselfabout an annular core, especially suited for preparing tape strips tomake the tape closure by simply severing said elongate strip of tape atright angles to the axis of the core at intervals corresponding to thepredetermined width of said closure, the length of each such closurecorresponding to width of the roll of tape, said composite elongatestrip of tape characterized by comprising in combination:

a. a fastening tape comprising an elongate strip of sheet backingmaterial, having first and second edges, being substantially as wide assaid composite strip, and having a layer of normally tacky anpressure-sensitive adhesive coated over at least substantially theentire width of said backing material.

b. the adhesive of said fastening tape adjacent the first edge thereofcontacting and adhered to the back of a pressure-sensitive adhesivetarget tape.

c. the adhesive of said fastening tape adjacent the second edge thereofcontacting and adhered to the back of a pressure-sensitive adhesiverelease tape, at least one of said tapes comprising a paper backinghaving a release coating of solventless, radiation-cured siliconeapplied directly to the paper. This construction is in accordance withEuropean Patent No. 0148587.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to the accompanyingdrawing which represents a cross-section through a laminate tapeconstruction in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The composite tape is subdivided into bonded section (16) and fasteningsection (17) and made up of fastening tape (12), target tape (18),release tape (21) and unifying strip (24).

Fastening tape (12) comprises any suitable paper backing (13) provided arelease coating of a solventless, radiation-cured silicone applieddirectly to the paper to facilitate unwinding of the composite tape whenwound upon itself about the core. One face of the backing (13) is coatedwith a layer (15) of a tacky and aggressive pressure-sensitive adhesive.Suitable adhesives include conventional rubber-resin adhesives whichhave tack characteristics modified by the inclusion of tackifying resinssuch as the tackifying resins described in U.S. Pat. No. 4,136,071. Theaggressive pressure-sensitive adhesives used for layer (15) may alsoinclude conventional rubber-resin adhesives modified to have peelstrengths between about 6 and 10 newtons per 25 mm, preferably about 8newtons per 25 mm. A suitable method for measuring the peel strengths ofadhesive layers on a steel, polyethylene or polypropylene surface isdescribed in U.S. Pat. No. 4,801,480.

Target tape (18), formed of any suitable tape backing material, ispositioned so that it coincides with and covers part of adhesive layer(15). The top surface of target tape (18) is releasably adhered toadhesive layer (15). The bottom surface of target tape (18) is coatedwith a layer (19) of normally tacky and pressuresensitive adhesive. Thisadhesive layer (19) must form a strong shear bond to the outer surfaceof the diaper where it is adhered during use and may be the same asadhesive layer (15).

A first fingerlift (20) is positioned between fastening tape (12) andtarget tape (18). The first fingerlift (20) is adhered to fastening tape(12) by adhesive layer (15). Fingerlift (20) facilitates the Lifting offastening tape (12) from the target tape (18).

Release tape (21), formed of any suitable tape backing material, ispositioned such that it substantially covers and is adhered to adhesivelayer (19). The top surface of release tape (21) may be provided with acoating of release agent so that target tape (18) may be readilyseparated from release tape (21).

A second fingerlift (23) is adhesively attached to target tape (18) byadhesive layer (19). The fingerlift (23) is attached to an end portionof target tape (18) and facilitates the separation of target tape (18)from release tape (21) in order to allow initial positioning of targettape (18) and fastening tape (12) on the opposed side of the diaper.

Fingerlifts (20, 23) which are typically formed of narrow strips ofpolymeric film, are adhered to backing (13) and target tape (18) byadhesive layers (15, 19 respectively). The fingerlifts (20, 23) extendoutwardly beyond the edge of fastening tape (12) and target tape (18) topermit and facilitate the separation of the various tapes. Theseparation of fastening tape (12) from target tape (18) is facilitatedwhen it is desired to reopen the diaper closure.

Unifying strip (24), typically formed of a narrow strip of the samematerial as fingerlifts (20, 23) is positioned between end portions oftape such that its centerline coincides with the junction of target tape(18) and release tape (21) and adhesive layers (15, 19, 22). Thus, onepart of unifying strip (24) is adhered to adhesive layer (22) and anapproximately equal part is adhered to adhesive layer (15).

U.S. Pat. No. 4,801,480 illustrates the use of closures formed bysevering such a composite tape at intervals corresponding to thepredetermined width of the closure, parallel to the axis of the tapecore.

What is claimed is:
 1. A laminate tape construction comprising two ormore porous paper backed tapes each of said porous paper backed tapeshaving a layer of pressure-sensitive adhesive in which at least one ofsaid tapes comprises a porous paper backing without any barrier layer,said at least one tape having two opposite faces, a first face having afirst pressure-sensitive adhesive layer adhered directly thereto and afirst continuous release coating of a solventless, radiation-curedsilicone applied directly to the porous paper backing second face, thepenetration of the silicone into the porous paper backing being suchthat silicone is not on the porous paper backing first face, which paperbacking has a basis weight of from 50 to 150 g/m².
 2. The laminate tapeconstruction as claimed in claim 1 wherein said porous paper backed tapelaminate comprises(1) a fastening tape, divided into a bonded sectionand a fastening section, said fastening tape comprising an elongatedstrip of said porous paper backing, having first and second edges, beingsubstantially as wide as said tape laminate and having a layer ofpressure-sensitive adhesive forming said first pressure-sensitiveadhesive layer coated over said first face of said fastening tape porousbacking, and said first continuous release coating applied over saidsecond face, (2) a target tape, having first and second faces, first andsecond edges, the target tape first adhered to said firstpressure-sensitive adhesive layer, a second layer of pressure-sensitiveadhesive coated on the second face of the target tape, (3) a releasetape, having first and second faces, the first face adhered to saidsecond pressure-sensitive adhesive layer; a third layer ofpressure-sensitive adhesive coated on the second face of said releasetape, and (4) a unifying strip centered over an edge of said releasetape and adhered to the third pressure-sensitive adhesive layer on saidrelease tape and to the first pressure-sensitive adhesive layer on saidfastening tape.
 3. A laminate tape construction as claimed in claim 2 inwhich a first fingerlift is interposed between the first adhesive layerand the target tape at the second edge of said fastening tape and asecond fingerlift is interposed between the second pressure-sensitiveadhesive layer and the release tape at the second edge of the targettape.
 4. A laminate tape construction as claimed in claim 2 in which theporous paper backing of the fastening tape is free from adhesive at thesecond edge to provide said first fingerlift.
 5. A laminate tapeconstruction as claimed in claim 1 in which the paper backing has abasis weight of from 80 to 110 g/m².
 6. A laminate tape construction asclaimed in claim 1 in which the coating weight of the release coating isfrom 0.4 to 2.0 g/m².
 7. A laminate tape construction as claimed inclaim 1 in which the pressure-sensitive adhesive is a hot melt adhesiveor a solvent based adhesive.
 8. A laminate tape as claimed in claim 1 inwhich the peel strength of the pressure-sensitive adhesive on saidsilicone release layer is from 0.1 to 3.0 newtons per 25 mm width.
 9. Alaminate tape as claimed in claim 1 in which the paper backing iscolored and/or bears printed indicia.